Why Most UK Business Sales Fail During Due Diligence and How to Avoid It

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Accountant

Post Date

Feb 01, 2026

UK business sale due diligence preparation and checklist

For many business owners, agreeing a headline price feels like the moment the sale becomes real.

Heads of Terms are signed. Advisers are instructed. The buyer has committed time and resources to the transaction.

It is tempting to think the hardest part is over.

In reality, this is often where the most detailed scrutiny begins.

Once due diligence starts, the buyer moves from assessing the opportunity at a high level to testing the information behind it. Financial records are examined in greater detail. Contracts are reviewed. Tax matters are investigated. Customer relationships, employees, intellectual property and operational processes may all come under scrutiny.

Questions that seemed relatively unimportant during early negotiations can suddenly become material.

A missing contract may require legal advice. An unexplained accounting adjustment can lead to further financial investigation. A customer concentration issue may change the buyer’s assessment of future revenue. A historic compliance matter may require additional protection in the transaction documents.

None of this necessarily means the business is fundamentally flawed.

The problem is usually uncertainty that has been discovered too late.

That is why preparation for due diligence should begin well before a buyer starts asking questions.

What Due Diligence Actually Means for a Buyer

Due diligence is sometimes viewed by sellers as a lengthy checklist that must simply be completed before the deal can close.

For the buyer, it serves a much more important purpose.

It is an opportunity to verify whether the business they believe they are acquiring is actually the business represented during negotiations.

A buyer is effectively testing several assumptions:

  1. Are the reported financial results reliable?
  2. Is the current level of trading sustainable?
  3. Are important customer relationships secure?
  4. Does the company own the assets it claims to own?
  5. Are there liabilities that have not been disclosed?
  6. Can the business continue operating effectively after completion?
  7. Are there legal, tax or regulatory matters that could affect future performance?

The buyer’s advisers will approach these questions from different perspectives.

The accountant may focus on earnings, working capital and cash flow.

The solicitor may examine contracts, ownership, employment matters and potential liabilities.

Tax advisers may investigate historic tax positions and areas of exposure.

Commercial advisers may examine customers, suppliers, market position and operational resilience.

The seller therefore needs to understand that due diligence is not one investigation.

It is a series of investigations designed to build a reliable picture of the business.

Why Deals Can Change After Heads of Terms

Heads of Terms normally establish the broad commercial understanding between the parties.

They can cover matters such as the proposed price, transaction structure, timetable and other principal terms.

But they do not remove the buyer’s need to investigate the business.

This creates an important distinction.

The buyer may have agreed a price based on the information available at that point.

If subsequent investigation reveals something materially different, the buyer may reconsider the assumptions behind that price.

For example, imagine that a business is presented as having stable earnings.

During financial due diligence, the buyer discovers that a significant proportion of recent profit came from non-recurring work.

The business may still be attractive.

But the buyer now has a different understanding of maintainable performance.

Similarly, a company may appear to have strong customer retention until the buyer discovers that one major customer can terminate its agreement shortly after completion.

Again, the business hasn’t suddenly become worthless.

The buyer has simply learned something that affects the risk they are taking.

This is why the quality of information presented before and during due diligence matters so much.

Not every issue discovered during due diligence will cause a transaction to fail.

Businesses are complicated.

Historical issues exist. Contracts have limitations. Forecasts are never certain. Customers can leave. Employees can depart.

Buyers understand this.

What creates considerably more difficulty is discovering a material issue that the seller appeared not to know about—or knew about but failed to disclose.

Consider two situations.

In the first, the seller tells the buyer early that a major customer is renegotiating its contract. The seller provides the background, explains the relationship, and gives the buyer the relevant documentation.

The buyer can assess the situation.

In the second, the buyer discovers the renegotiation independently during their own review.

The original commercial issue may be identical.

The difference is trust.

The second situation can lead to a much broader question:

If this wasn’t disclosed, what else might we discover?

That is why transparency is so important during a transaction.

Early disclosure gives advisers an opportunity to assess and manage an issue.

Late discovery can make the same issue appear significantly more serious.

The Six Areas Most Likely to Attract Difficult Questions

There is no universal due-diligence checklist that applies identically to every UK business.

A regulated financial services company, for example, will face different questions from a manufacturing business or a professional services firm.

However, several areas appear consistently across transactions.

These include:

  1. Financial reporting and maintainable earnings
  2. Previously undisclosed problems
  3. Dependence on the owner or key individuals
  4. Contracts, intellectual property and legal documentation
  5. Customer concentration and revenue durability
  6. Seller readiness and behaviour during the transaction

The significance of each issue depends on the business.

The important point is not to assume that a buyer will overlook something simply because it has never caused an operational problem before.

Due diligence changes the level of scrutiny.

Reason #1 — Financial Information That Does Not Stand Up to Scrutiny

Financial information is usually one of the first areas to receive detailed attention.

A buyer isn’t simply interested in the profit figure shown in the accounts.

They want to understand how that profit was generated, whether it is repeatable, and whether the underlying financial position supports the assumptions used to agree the transaction.

This is where inconsistencies can become particularly damaging.

A business may have perfectly legitimate reasons for differences between management accounts and statutory accounts.

There may be timing differences, year-end adjustments, exceptional expenditure or accounting treatments that require explanation.

The existence of an adjustment isn’t necessarily the problem.

The problem is being unable to explain it clearly.

Financial Issues That Commonly Trigger Further Questions

Buyers and their advisers may investigate:

  1. Differences between management and statutory accounts
  2. Unusual or unsupported add-backs
  3. Owner-related expenditure
  4. Revenue recognition
  5. Gross-margin movements
  6. Working-capital fluctuations
  7. Exceptional items
  8. Cash-flow performance
  9. Forecast assumptions
  10. Significant changes between reporting periods

The buyer is trying to establish whether the financial information presents a dependable picture of the company’s underlying performance.

If the numbers reconcile and the explanations are supported by evidence, questions can usually be dealt with efficiently.

If the numbers repeatedly require correction, the process becomes much more difficult.

Why Financial Consistency Matters

Imagine a buyer receives three different versions of the company’s recent performance.

The management accounts show one level of profit.

The forecast uses another.

The statutory accounts later reveal something different again.

There may be legitimate explanations for each figure.

But the buyer now has to spend additional time determining which information should be relied upon.

That creates friction.

It can also affect the buyer’s confidence in other information supplied by the seller.

Financial due diligence therefore isn’t just about whether the business makes money.

It is also about whether the seller can demonstrate the financial position clearly and consistently.

How to Prepare Before the Buyer Starts

A seller should ideally conduct an internal review of the financial information before entering detailed negotiations.

Useful preparation can include:

  • Reconciling management accounts with statutory accounts
  • Reviewing unusual transactions
  • Documenting the basis for significant adjustments
  • Separating recurring and non-recurring items
  • Reviewing recent cash-flow performance
  • Testing forecast assumptions against historical performance
  • Ensuring supporting documentation is readily available

Where appropriate, an accountant or corporate finance adviser can help identify areas that are likely to receive additional scrutiny.

The objective is not to make the accounts look better.

It is to make the financial story clear, consistent and defensible.

That distinction is critical.

Reason #2 — Problems That Are Discovered Too Late

The second major source of difficulty is the late discovery of issues that could have been disclosed or addressed earlier.

Almost every established business has something that requires explanation.

There may be:

  • A historic customer dispute
  • A tax enquiry
  • An employment matter
  • A regulatory issue
  • A supplier disagreement
  • A contractual problem
  • An unresolved complaint
  • A potential liability

The presence of an issue does not automatically make a business unsaleable.

The way the issue is handled can be far more important.

Why Late Disclosure Creates a Bigger Problem

Suppose the seller knows about an ongoing dispute and tells the buyer at the appropriate stage.

The buyer’s solicitor can investigate it, assess the potential exposure and determine whether specific contractual protection is required.

That is manageable.

Now imagine the buyer discovers the dispute independently after several weeks of due diligence.

The buyer is likely to ask why it wasn’t disclosed earlier.

The issue has now become two questions:

What is the underlying risk?

and

Why wasn’t this information provided earlier?

The second question can be more damaging than the first.

Trust is an important component of any acquisition.

Once the buyer begins questioning whether information is being disclosed completely, they may expand their investigation into other areas.

How Sellers Should Handle Known Issues

Before entering a transaction, create an internal list of matters that could reasonably attract buyer questions.

Review areas such as:

  1. Current or historic disputes
  2. Tax correspondence
  3. Regulatory matters
  4. Employee claims
  5. Major customer complaints
  6. Contractual breaches
  7. Insurance claims
  8. Potential liabilities

Material issues should be discussed with the appropriate professional adviser.

The objective isn’t to overwhelm a buyer with irrelevant information.

It is to ensure that significant matters are disclosed accurately, with enough context for them to be assessed properly.

A manageable problem disclosed early is usually easier to deal with than the same problem discovered unexpectedly.

Reason #3 — The Business Relies Too Heavily on the Owner

A business can perform exceptionally well while still creating a significant concern for a prospective buyer: too much of its knowledge, decision-making and commercial relationships sit with the owner.

This often develops naturally.

The founder wins the first customers, negotiates important contracts, solves operational problems and becomes the person everyone turns to when something goes wrong.

Over time, the business may become highly dependent on that individual.

During normal trading, this may not appear to be a weakness.

During due diligence, it becomes much easier to identify.

What Buyers Are Trying to Establish

A buyer will want to understand what happens when the current owner is no longer running the company.

They may examine:

  1. Who manages the largest customer relationships
  2. Who makes important operational decisions
  3. Where key commercial knowledge is held
  4. Whether senior employees have genuine authority
  5. How processes are documented
  6. Whether the management team can operate independently
  7. What role the seller expects to have after completion

The question underneath all of these enquiries is straightforward:

Can the business continue performing when ownership changes?

If the answer depends heavily on the seller remaining involved, the buyer may need to reconsider the transition risk.

How to Reduce the Concern Before Sale

Owner dependency cannot usually be removed through a document prepared immediately before a transaction.

It needs to be reduced through actual changes in the business.

Useful steps can include:

  1. Giving senior managers greater decision-making authority
  2. Introducing clearer management responsibilities
  3. Documenting important operational procedures
  4. Building customer relationships across the wider team
  5. Sharing critical commercial knowledge
  6. Cross-training employees
  7. Reducing unnecessary approval bottlenecks

The strongest evidence is behavioural.

If the owner can genuinely step away for an extended period and the business continues operating normally, that tells a buyer considerably more than a statement claiming the company is not dependent on its founder.

Reason #4 — Contracts, Intellectual Property and Legal Records Contain Gaps

Legal due diligence can uncover issues that have never caused a problem during normal trading.

A company may have used the same customer agreement for years without considering what happens if the business is sold.

A contractor may have created intellectual property without an appropriately drafted agreement.

A software licence might be registered to an individual rather than the company.

An important contract may contain a change-of-control provision that nobody has previously considered.

These matters become relevant because ownership is about to change.

Areas That Deserve an Early Review

Before entering a transaction, sellers should consider reviewing:

  1. Major customer contracts
  2. Supplier agreements
  3. Property leases
  4. Employment agreements
  5. Contractor arrangements
  6. Intellectual property ownership
  7. Software and technology licences
  8. Brand and trademark ownership
  9. Domain ownership
  10. Insurance policies
  11. Regulatory licences
  12. Data protection arrangements
  13. Existing or historic disputes

The exact scope will depend on the nature of the company.

A regulated business, for example, may face substantially different requirements from a professional services company.

Change of Control Clauses Deserve Particular Attention

One issue that can be overlooked is whether a contract can continue after a change in ownership.

Some agreements contain provisions requiring the other party’s consent before the contract can be transferred or the company can undergo a change of control.

If a major revenue-generating agreement is affected, this can become commercially significant.

Finding the clause months before a sale gives the seller and advisers time to determine the appropriate response.

Finding it after a buyer has already committed resources to the transaction creates considerably more pressure.

That is why legal preparation should happen before the formal due-diligence process begins.

Reason #5 — Customer Concentration Creates Questions About Future Revenue

Strong turnover doesn’t necessarily mean predictable revenue.

A buyer will want to understand where that revenue comes from and how much of it depends on a small number of relationships.

For example, a company generating £5 million in annual revenue may initially look very different from another company generating the same amount if one-third of that revenue comes from a single customer.

The issue isn’t automatically the concentration itself.

It is the potential impact if that relationship changes.

Questions Buyers May Ask

During commercial due diligence, buyers may investigate:

  1. The percentage of revenue generated by major customers
  2. Customer retention rates
  3. Length of key relationships
  4. Contract duration
  5. Renewal arrangements
  6. Termination provisions
  7. Historical customer losses
  8. Whether relationships depend on the owner
  9. The likelihood of customers remaining after completion

This allows the buyer to distinguish between concentrated but secure revenue and concentrated and vulnerable revenue.

Those are very different situations.

How Sellers Can Prepare

If customer concentration is already significant, trying to hide the issue is unlikely to help.

Instead, demonstrate that the exposure is understood.

Relevant evidence could include:

  1. Historical retention information
  2. Contractual arrangements
  3. Renewal history
  4. Customer relationship records
  5. Evidence of service performance
  6. Relationships between customers and the wider management team
  7. A credible strategy for reducing concentration over time

A buyer doesn’t necessarily expect every commercial risk to disappear.

They want to understand the risk well enough to make an informed decision.

Reason #6 — Seller Fatigue Can Affect the Final Stages of a Deal

The final issue is less tangible but still important.

Due diligence can be demanding.

By this stage, the seller may have spent months answering questions, providing documents, attending meetings and negotiating with advisers.

The initial excitement of selling the business can be replaced by fatigue.

That can affect judgement.

A seller may become frustrated by repeated information requests or interpret routine questions as criticism.

Others may become so eager to complete that they stop paying attention to important details.

Neither reaction helps.

Why Seller Behaviour Matters

Buyers are assessing more than the documents.

They are also forming an impression of how the transaction will work after completion.

If reasonable questions repeatedly receive defensive responses, or information is supplied slowly and inconsistently, the buyer may begin to question how difficult the transition will be.

This doesn’t mean sellers should agree with every request.

It means disagreements should remain commercial and evidence-based.

Use Advisers Properly

Professional advisers should not simply be used to review documents.

They can also create a useful buffer between the seller and the buyer’s advisers.

Accountants can handle financial questions.

Solicitors can address legal matters.

Corporate finance advisers can help interpret commercial requests and manage negotiations.

This allows the owner to remain focused on running the business while ensuring that difficult questions are handled professionally.

The seller’s role is not to win every conversation.

It is to keep the transaction moving while protecting their interests.

How Preparation Can Prevent Due Diligence Problems

The common thread across these issues is timing.

A problem discovered twelve months before a transaction is different from the same problem discovered two weeks before completion.

Early preparation gives the seller choices.

They may be able to:

  1. Correct an issue
  2. Obtain missing documentation
  3. Renegotiate a contract
  4. Strengthen management structures
  5. Improve reporting
  6. Obtain professional advice
  7. Disclose an issue with appropriate context
  8. Decide whether a particular weakness should be addressed before going to market

Late discovery removes many of those options.

This is why due diligence should be treated as something you prepare for, rather than something you simply respond to.

A Practical Pre-Due-Diligence Review

Before approaching buyers, it is worth looking at the business as though you were conducting the buyer’s investigation yourself.

Ask the following questions.

Financial

Can every significant figure be explained?

Do management accounts, statutory accounts and supporting records tell the same story?

Commercial

Which customers generate the most revenue?

How secure are those relationships?

Legal

Are important agreements complete, current and appropriately structured?

People

Could the business continue operating if the owner disappeared from the day-to-day operation tomorrow?

Tax and Compliance

Are there historic matters that could reasonably attract professional scrutiny?

Documentation

Could the company respond efficiently if a buyer requested hundreds of documents?

Disclosure

Are there known issues that should be discussed with advisers before they become buyer discoveries?

This exercise isn’t about making the company appear flawless.

It is about understanding the business from the other side of the transaction.

Due Diligence Should Confirm the Deal Not Rewrite the Story

The strongest position for a seller is to enter due diligence with a business that has already been examined internally.

That doesn’t mean every question will have an easy answer.

There will almost always be additional requests.

There may be negotiations.

There may be matters that require professional advice or changes to the transaction documents.

That is normal.

The objective is to prevent avoidable surprises from changing the buyer’s understanding of the business.

A buyer should ideally reach the end of due diligence thinking:

“We’ve investigated the business and understand the risks.”

Not:

“We’re still discovering what we’re actually buying.”

That difference can determine whether a transaction progresses smoothly or begins to unravel.

What to Do When Due Diligence Uncovers a Problem

Finding an issue during due diligence does not automatically mean the transaction is in trouble.

The response matters.

A common mistake is to react immediately either by becoming defensive or by trying to minimise the issue. Both approaches can make a manageable problem more difficult.

Instead, establish three things:

  1. What exactly has been identified?
  2. How material is it to the business or transaction?
  3. What evidence, explanation or remedy is available?

For example, an outdated employment agreement is a different issue from a significant employment claim. A customer concentration problem is different from a customer actively preparing to terminate its contract.

The buyer’s advisers need enough information to assess the actual risk.

Don't Hide a Problem Once It Has Been Identified

If an issue is genuine and material, attempting to conceal it is rarely a sensible strategy.

The buyer may discover it through another source anyway.

Instead, work with the appropriate adviser to establish:

  • The facts
  • The financial or operational impact
  • Whether the issue can be resolved
  • What documentation supports the position
  • Whether additional contractual protection may be required

A difficult fact presented clearly is generally easier to manage than a difficult fact discovered unexpectedly.

Not Every Due-Diligence Request Is a Negotiation

Sellers can sometimes become frustrated when the buyer continues asking questions after the commercial terms have been broadly agreed.

It is important to distinguish between verification and renegotiation.

A buyer’s accountant asking for evidence supporting an adjustment isn’t necessarily trying to reduce the purchase price.

A solicitor requesting a contract isn’t necessarily looking for a reason to terminate.

An adviser asking about a historic tax matter isn’t necessarily suggesting that the business has a tax problem.

Many requests are simply part of establishing whether the information provided during negotiations is accurate.

How to Respond Efficiently

When a request arrives, establish:

  • What information has actually been requested?
  • Which person has the answer?
  • Is supporting evidence available?
  • Does the question require specialist advice?
  • Is there a material issue that needs to be escalated?

Answer the question directly where possible.

If the answer is uncertain, don’t guess.

It is better to say that the matter is being verified than to provide an inaccurate answer that creates another problem later.

What Sellers Should Avoid During Due Diligence

There are several behaviours that can unnecessarily increase transaction risk.

Avoid Delaying Straightforward Requests

A document that takes five minutes to provide should not remain outstanding for several days without a reason.

Repeated delays can create the impression that information is difficult to obtain.

Avoid Changing the Numbers Without Explanation

If a figure supplied earlier needs to be corrected, explain why.

A correction with a clear explanation is manageable.

A changing figure with no explanation creates uncertainty.

Avoid Overpromising Future Performance

Forecasts should be supported by realistic assumptions.

A buyer will usually test ambitious projections against historical performance, market conditions and the company’s actual capacity to deliver growth.

Avoid Taking Every Question Personally

Due diligence is scrutiny of the business, not necessarily criticism of the seller.

The buyer is committing significant capital.

They are entitled to understand what they are purchasing.

Avoid Making Material Decisions Without Advice

Changes to contracts, disclosures, warranties, tax positions or transaction terms can have consequences beyond the immediate question.

Where an issue is material, involve the appropriate professional adviser before responding.

A 30/60/90-Day Preparation Framework

If a transaction is approaching, preparation can be structured into three stages.

90 Days Before — Identify the Weak Points

Start with a broad review of the business.

Look at:

  • Financial reporting
  • Customer concentration
  • Key contracts
  • Intellectual property
  • Employment documentation
  • Tax matters
  • Regulatory compliance
  • Management structure
  • Owner dependency
  • Outstanding disputes

The objective at this stage is identification, not perfection.

You want to know where questions are likely to arise while there is still time to address them.

60 Days Before — Resolve and Organise

Once the major areas have been identified, begin addressing the practical issues.

For example:

  • Reconcile financial information
  • Locate missing contracts
  • Update relevant documentation
  • Review significant customer agreements
  • Clarify ownership of intellectual property
  • Address outstanding compliance matters
  • Organise corporate records
  • Document important operational processes

This is also a useful point to establish responsibility for different categories of information.

Someone should know who owns the financial information.

Someone should know where the legal documents are.

Someone should know who can answer operational questions.

30 Days Before — Test Your Readiness

The final stage should be about testing whether the business can actually respond efficiently.

Ask a simple question:

“If the buyer requested this information tomorrow, could we provide it accurately?”

Run through the likely information categories.

Test whether:

  • Financial records reconcile
  • Key documents are accessible
  • Major contracts can be located quickly
  • Management information is current
  • Known issues have been discussed with advisers
  • Responsibilities are clearly allocated
  • The business can continue operating while management handles the transaction

If the answer is no, there is still useful work to do.

UK Business Sale Due-Diligence Readiness Checklist

Before detailed due diligence begins, sellers should consider whether they can answer yes to the following.

AreaReadiness question
FinancialCan the company’s recent financial performance be clearly explained?
Cash flowCan recent cash movements and working-capital changes be supported?
CustomersAre major customer relationships understood and documented?
ContractsAre important commercial agreements available and current?
LegalHave material disputes and potential liabilities been identified?
EmployeesAre key employment arrangements properly documented?
IPCan ownership of important intellectual property be demonstrated?
TaxHave relevant historic and current tax matters been reviewed?
OperationsCan the business operate without excessive dependence on the owner?
ManagementIs there sufficient leadership capacity for the transition?
ComplianceAre relevant licences, policies and regulatory obligations in order?
DocumentationCan requested information be produced without unnecessary delay?
DisclosureAre known material issues understood and ready to be discussed appropriately?

This isn’t a substitute for legal, tax or financial advice.

It is a practical way of identifying areas that deserve attention before the buyer starts asking the questions.

Preparation Protects More Than the Transaction

The value of preparation isn’t limited to preventing a buyer from walking away.

It can also protect the commercial terms that were originally agreed.

When due diligence reveals unexpected problems, the buyer may seek additional protection or revisit aspects of the transaction.

That can take the form of:

  1. Price adjustments
  2. Specific warranties
  3. Indemnities
  4. Retentions
  5. Escrow arrangements
  6. Changes to completion conditions
  7. Additional transitional arrangements

None of these outcomes is inevitable.

But the more uncertainty the buyer encounters, the greater the possibility that the transaction structure will change.

Good preparation therefore isn’t simply about getting the deal completed.

It is about entering negotiations with a clear understanding of the business and fewer avoidable weaknesses.

Final Thoughts

Most problems encountered during due diligence do not appear overnight.

They usually existed long before the buyer arrived.

The difference is that a transaction forces the business to examine them under a much brighter light.

Financial inconsistencies, incomplete documentation, customer concentration, owner dependency and historic legal or tax matters may have been manageable during normal trading.

Once ownership is changing, however, the buyer needs to understand exactly what they are taking on.

That is why preparation should begin before Heads of Terms rather than after them.

A well-prepared seller doesn’t need to pretend the business has no weaknesses.

They need to understand those weaknesses, deal with what can be fixed, document what can be evidenced and explain what remains.

The strongest transactions are rarely the ones where no difficult questions are asked.

They are the ones where difficult questions have clear, credible answers.

Due diligence should ultimately confirm the buyer’s decision not force them to rethink what they believed they were buying.

Frequently Asked Questions

Q1. When should a UK business start preparing for due diligence?

Ideally, preparation should begin several months before approaching buyers. This gives the owner time to identify financial, legal, operational and commercial issues while there is still an opportunity to address them.

Q2. Can a business sale still complete if problems are found during due diligence?

Yes. Finding an issue does not automatically mean a transaction will fail. The outcome depends on the nature of the issue, its potential impact, whether it was disclosed appropriately and how the buyer and advisers agree to manage the risk.

Q3. What financial information do buyers usually examine?

The exact scope varies, but buyers may review statutory accounts, management accounts, cash flow, forecasts, working capital, revenue trends, margins, debt and significant adjustments to reported earnings.

Q4. Why is owner dependency a concern during a business sale?

A buyer needs confidence that the business can continue operating after the current owner exits. If important customers, decisions, processes or knowledge depend heavily on one individual, the transition may carry greater operational risk.

Q5. Does customer concentration automatically reduce a business's value?

Not necessarily. A concentrated customer base can be more manageable when relationships are long-standing, contractual and supported by the wider management team. The buyer will generally assess the quality and durability of the revenue rather than relying on concentration alone.

Q6. What should a seller do if they discover a problem before the buyer does?

First establish the facts and potential impact. Then discuss the matter with the appropriate professional adviser. Where disclosure is required, provide accurate information and appropriate context rather than waiting for the buyer to discover the issue independently.